Process for making an abrasion resistant quasi monofilament

Abstract

A quasi monofilament having a high strength polyethylene fiber core with an adherent, abrasion resistant polymer sheath is prepared by feeding the core yarn through a crosshead die, while simultaneously supplying a polymer melt at a temperature greater than the melting point of the core yarn to the die, for sheathing the core yarn within the die with the melt under a sufficient pressure to cause the melt to adhere to the core yarn. The abrasion resistant polymer sheath includes an effective amount of a first polymer having ethylene crystallinity, a density of at least about 0.94 g/cm 3 , and a melt index of less than about 0.1 g/10 min. The composition used to sheathe the core yarn is characterized by a weight average tensile strength at yield of greater than about 13.8 MPa. The quasi monofilament has utility in applications subjected to high abrasion, such as sports fishing lines, kite lines, dental floss, "weedeater" lines and tennis racket strings.

We claim: 
     
       1. A process for making an abrasion resistant quasi monofilament, comprising the steps of: a. continuously feeding a core polyethylene multi-filament yarn having a tenacity of at least about 15 g/d and a tensile modulus of at least about 500 g/d through a crosshead die, while simultaneously   b. supplying a polymer melt at a temperature greater than the melting point of the core yarn to the die, for   c. sheathing the core yarn within the die with the melt under a sufficient pressure to cause the melt to adhere to the core yarn; and   d. cooling the sheathed yarn to below the melting point of the polymer melt.   
     
     
       2. The process of claim 1 wherein the yarn is fed at a yarn velocity of up to about 900 m/min, the yarn has a residence time in the die of up to about 0.10 sec., and the melt is supplied at a melt throughput sufficient to form from about 10 to about 90 weight percent of the sheathed core yarn. 
     
     
       3. The process of claim 2 wherein the yarn is fed at a yarn velocity of about 150 to about 600 m/min, the yarn has a residence time in the die of about 0.01 to about 0.05 sec., and the melt is supplied at a melt throughput sufficient to form from about 15 to about 60 weight percent of the sheathed core yarn. 
     
     
       4. The process of claim 2 wherein the melt is supplied at a melt throughput sufficient to form from about 20 to about 45 weight percent of the sheathed core yarn. 
     
     
       5. The process of claim 1 wherein the temperature is at least about 25° C. above the melting point of the core yarn and the melt is under a pressure of at least about 3.4 MPa at the melt entrance to the crosshead die. 
     
     
       6. The process of claim 5 wherein the temperature is at least about 50° C. above the melting point of the core yarn. 
     
     
       7. The process of claim 1 additionally comprising the step of twisting the core yarn prior to the feeding step. 
     
     
       8. The process of claim 7 wherein the core yarn is twisted with about 0.1 to about 20 tpi. 
     
     
       9. The process of claim 8 wherein the core yarn is twisted with about 0.5 to 15 tpi. 
     
     
       10. The process of claim 7 additionally comprising the step of post-stretching the sheathed core yarn at a temperature within about 10° C. of the melting point of the core yarn at a rate of less than about 1 sec -1 . 
     
     
       11. The process of claim 7 additionally comprising the step of pretreating the core yarn prior to the feeding step to enhance adherence of the melt to the core yarn. 
     
     
       12. The process of claim 11 wherein the pretreating step comprises priming the surface of the core yarn with an effective amount of a resin having ethylene crystallinity and a melting point of less than about 135° C. 
     
     
       13. The process of claim 11 wherein the pretreating step comprises priming the surface of the core yarn with an effective amount of mineral oil. 
     
     
       14. The process of claim 11 wherein the pretreating step comprises corona treatment of the core yarn. 
     
     
       15. The process of claim 14 wherein the pretreating step further comprises priming the surface of the core yarn with an effective amount of a resin having ethylene crystallinity and a melting point of less than about 135° C. after corona treatment. 
     
     
       16. The process of claim 11 wherein the pretreating step comprises plasma treatment of the core yarn. 
     
     
       17. The process of claim 11 wherein the pretreating step comprises scouring the core yarn. 
     
     
       18. The process of claim 11 wherein the melt is supplied at a melt throughput sufficient to form from about 15 to about 60 weight percent of the sheathed core yarn, the temperature is at least about 25° C. above the melting point of the core yarn, the pressure is at least about 3.4 MPa at the melt entrance to the crosshead die, and the core yarn is twisted with about 0.1 to about 20 tpi. 
     
     
       19. The process of claim 18 wherein the melt is supplied at a melt throughput sufficient to form from about 20 to about 45 weight percent of the sheathed core yarn, the temperature is at least about 50° C. above the melting point of the core yarn, and the core yarn is twisted with about 0.5 to about 15 tpi. 
     
     
       20. The process of claim 7 wherein the melt is supplied at a melt throughput sufficient to form from about 15 to about 60 weight percent of the sheathed core yearn, the temperature is at least about 25° C. above the melting point of the core yarn, the pressure is at least about 3.4 MPa at the melt entrance to the crosshead die, and the core yarn is twisted with about 0.1 to about 20 tpi. 
     
     
       21. The process of claim 20 wherein the melt is supplied at a melt throughput sufficient to form from about 20 to about 45 weight percent of the sheathed core yarn, the temperature is at least about 50° C. above the melting point of the core yarn, and the core yarn is twisted with about 0.5 to about 15 tpi. 
     
     
       22. The process of claim 1 additionally comprising the step of pretreating the core yarn to enhance adherence of the melt to the core yarn.